Subsea well drilling and production are complex and dangerous operations. One such danger is a blowout of the well. A blowout is the uncontrolled release of crude oil and/or natural gas (hydrocarbon) from an oil well when formation pressure exceeds the pressure applied to it by the column of drilling fluid. Typically, a blowout occurs as a result of pressure control systems failure, or loss of containment, of a surface well due to natural disaster or other event.
A conventional well includes an array of equipment designed and operated to prevent blowouts. One example of such equipment is a blowout preventer (BOP). Generally, the first line of defense in well control is to properly maintain the balance of mud in the wells circulatory system to ensure that the hydrostatic weight, or pressure from the drilling fluid is equal or slightly greater than the pressure from the formation. When control of the formation pressure is not possible, the conventional second line of defense is the blowout preventer, which is part of the well. The BOP is a large set of valves that is connected to the wellhead. Further, the BOP can be operated remotely from the surface and is used in everyday drilling activities. The BOP can be closed in the event that control of the formation pressure is lost, and the well starts to flow uncontrollably.
Despite the wealth of conventional equipment, a blowout that disables or destroys well control equipment and facilities, particularly, equipment that disables the blowout preventer, production equipment, and associated systems, can result in substantial loss of oil and gas from the uncontrolled well and immeasurable environmental damage. In such emergency situations, well operators are left with few options, most of which are more theoretical than true and tested. As demonstrated by the British Petroleum blowout in the Gulf of Mexico (GOM), the options were either unrealistic, or when tried, ineffective.
One realistic option is the drilling of a relief well, which is a directional well that is drilled to intersect a well that is blowing out. The relief well is used to kill the uncontrolled well by injecting sufficient drilling fluid to drive back the flow of reservoir fluid. Drilling the relief well, however, is time-consuming, often requiring numerous weeks or months at a time where every minute of unabated oil and gas flow is costly and environmentally harmful.
In light of the above, there is a need for a faster, safer and more sure approach to access, control, and subsequently kill a blown-out, uncontrolled well that does not require a well's subsea or surface equipment to be operable after the blow out.